Very handy considering myself (and most people I know) have their HA+devices setup with as local-only. I don’t want my home automation connected to the internet at all, but I still want notifications if my kids room temps dropped too low or my garage door opens in the middle of the night.
I've been using the signal-cli add-on for this with a lot of success. I can add attachments, have the notifications show up on all my devices, and share a group with my partner so we both get the same notifications. All end-to-end encrypted.
What I also learned to enjoy about HA is the diversity of the community of users that found success in home automation without completely relying on "cloud" solutions. I think this is the ethos of this project: local control comes first.